This invention relates to an improvement in the treatment of cumene oxidation reaction mixture to raise the yields of phenol recoverable therefrom. More particularly, it relates to a process of decomposing cumene hydroperoxide and separating the decomposition product into its components comprising acetone, phenol and one or more by-products by fractional distillation wherein decomposition and fractional distillation are carried out under conditions such that dehydration of by-product dimethyl phenyl carbinol formed in the cumene oxidation step is substantially avoided with consequent reduction in formation of higher boiling by-products, such as alpha-methylstyrene dimers and cumyl phenol.
The production of phenol by oxidizing cumene with molecular oxygen in liquid phase in the presence or absence of added catalyst to obtain a solution of cumene hydroperoxide in cumene, followed by decomposition of the cumene hydroperoxide in the presence of catalysts, such as inorganic acids or SO.sub.2 to obtain decomposition product containing phenol and acetone, and subsequent fractional distillation to separate the decomposition product into its components comprising acetone and phenol products, has been described. Cumene oxidation with elemental oxygen, e.g. oxygen of air, yields as the principal oxidation products cumene hydroperoxide together with lesser amounts of dimethyl phenyl carbinol and acetophenone in varying proportions. Under acidic conditions in the subsequent decomposition reaction, substantial portions of the dimethyl phenyl carbinol are dehydrated to form alpha-methylstyrene, which, in the subsequent distillation step, can be recovered as a separate product. However, dimethyl phenyl carbinol which has not been dehydrated in the decomposition step will gradually dehydrate throughout the subsequent distillation procedure as a result of which recovery of pure phenol is complicated. Further, alpha-methylstyrene formed under such conditions tends to react with phenol to form cumyl phenol, thereby reducing the yield of phenol product. Since boiling point of dimethyl phenyl carbinol (202.degree. C.) is higher than that of phenol (boiling point 182.degree. C.), it remains with the phenol fraction even after removal of the alpha-methylstyrene fraction (boiling point 161.degree. C.) and continues to form alpha-methylstyrene within the phenol fraction after removal of the alpha-methylstyrene fraction. Since the alpha-methylstyrene so formed will remain with the phenol fraction, the purity of the phenol product is reduced. Further, under conventional conditions employed in fractionation of the cumene hydroperoxide decomposition product, alpha-methylstyrene tends to dimerize, forming a by-product for which there is no use.
Undesirability of presence of dimethyl phenyl carbinol during the distillation procedure has long been recognized. To remove the dimethyl phenyl carbinol, it has been proposed to dehydrate it during or subsequent to the cumene hydroperoxide decomposition step, but prior to separation of the alpha-methylstyrene fraction, as, e.g., by heating the decomposition product to elevated temperatures, preferably in the presence of acid catalysts. Under these conditions, however, dimerization of alpha-methylstyrene by-product and reaction of alpha-methylstyrene with phenol to form cumyl phenol tend to be favored, so that this method generally involves loss of desirable alpha-methylstyrene and phenol products.
It is known to neutralize the acid decomposition catalyst prior to subjecting the decomposition product to fractional distillation by methods such as passing the decomposition product over ion exchange resins, washing the decomposition product with water or alkali metal carbonate solutions, or adding alkali metal hydroxide in amount sufficient to neutralize the acid catalyst. It is known that presence of acid catalyst in the distillation procedure tends to catalyze formation of high boilers such as alpha-methylstyrene dimers and cumyl phenol.
In short, the prior art has attempted to solve the problems caused by presence of dimethyl phenyl carbinol in the cumene oxidation product, e.g. contamination of phenol product with alpha-methylstyrene, loss of alpha-methylstyrene by-product due to dimerization and loss of phenol product due to reaction of alpha-methylstyrene with phenol to form cumyl phenol, by dehydrating the dimethyl phenyl carbinol, and by neutralizing the acid decomposition catalyst, both prior to product distillation procedure.
It is an object of the present invention to provide an improved method for making phenol and acetone from cumene by oxidizing cumene to form cumene hydroperoxide, decomposing the cumene hydroperoxide to form a product comprising phenol and acetone, followed by fractional distillation to separate it into its components, wherein contamination of product phenol with alpha-methylstyrene is reduced, formation of high boiling by-products, such as alpha-methylstyrene dimers and cumyl phenol, is reduced, and wherein yields of product phenol are improved.